Link Paid Memberships Pro discount codes to affiliate accounts from another plugin/service.

pmpro_ld2aff.php

<?php
/*
Plugin Name: E20R - Link PMPro Discount Codes to Affiliate Accounts
Plugin URI: https://eighty20results.com/paid-memberships-pro/do-it-for-me/
Description: Link a PMPro Discount Code to the account of an affiliate 
Version: 1.0
Requires at least: 4.5
Tested up to: 4.9.8
Author: Eighty / 20 Results by Wicked Strong Chicks, LLC <thomas@eighty20results.com>
Author URI: https://eighty20results.com/thomas-sjolshagen/
License URI: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
License: GPLv2 or later
Text Domain: scba-customizations
Domain Path: /languages
*/

/*
 *	This is the parameter we're looking for to find affiliates
 *	Choose the 'define()' to uncomment, based on the plugin you are using to manage your affiliates
 */
define('PMPRO_LDC2AFF_KEY', 'wpam_id');		//Affiliates Manager Plugin
// define('PMPRO_LDC2AFF_KEY', 'pa');			//WordPress Lightweight Affiliates
// define('PMPRO_LDC2AFF_KEY', 'ref');			//AffiliateWP

/**
 * Get the values from options and make sure they are an array
 *
 * @return array
 */
function pmpro_ld2aff_getOptions() {
	
	$d2a = get_option('pmpro_ldc2aff', array());

	if(!is_array($d2a)) {
		$d2a = array();
	}

	return $d2a;
}

/**
 * Add a discount code/affiliate pair
 *
 * @param int 		$code_id
 * @param string|int 	$affiliate
 *
 */
function pmpro_ldc2aff_updateCode($code_id, $affiliate) {
	$d2a = pmpro_ld2aff_getOptions();

	if(empty($affiliate) && !empty($d2a[$code_id])) {
		unset($d2a[$code_id]);
		update_option('pmpro_ldc2aff', $d2a, 'no');
	} elseif(!empty($affiliate)) {
		$d2a[$code_id] = $affiliate;
		update_option('pmpro_ldc2aff', $d2a, 'no');
	}
}

/**
 * Get a discount code from an affiliate
 * 
 * @param string $affiliate
 *
 * @return int|string
 */
function pmpro_ldc2aff_getCodeByAffiliate($affiliate) {
	$d2a = pmpro_ld2aff_getOptions();

	return array_search($affiliate, $d2a);
}

/**
 * Get an affiliate id from a discount code
 *
 * @param int $code_id
 */
function pmpro_ldc2aff_getAffiliateByCode($code_id) {
	$d2a = pmpro_ld2aff_getOptions();

	if(isset($d2a[$code_id])) {
		return $d2a[$code_id];
	} 
	
	return "";

}

/**
 * Try to sync the affiliate id and discount code
 */
function pmpro_ldc2aff_init() {
	
	global $wpdb;

	// Cancel exeuction if key isn't set
	if ( ! defined( 'PMPRO_LDC2AFF_KEY' ) ) {
		return;
	}

	// Is PMPro active?
	if ( ! defined( 'PMPRO_VERSION' ) ) {
		return;
	}

	//TODO: Should check if the specifed affiliate plugin is also running

	// Have an affiliate id? Then set the/a discount code
	if( ! empty( $_REQUEST[ PMPRO_LDC2AFF_KEY ] ) ) {
		
		// Quit if another discount code is already set
		if( ! empty($_REQUEST[ 'discount_code' ] ) ) {
			return;		
		}

		// Let's figure out which code to use
		$affiliate = sanitize_text_field( $_REQUEST[ PMPRO_LDC2AFF_KEY ] );
		$code_id = pmpro_ldc2aff_getCodeByAffiliate( $affiliate );

		if( !empty( $code_id ) ) {
			
			$code = $wpdb->get_var(
				$wpdb->prepare( "SELECT dc.code FROM {$wpdb->pmpro_discount_codes} AS dc WHERE dc.id = %d LIMIT 1", $code_id )
			);
	
			$_REQUEST['discount_code'] 	= $code;
			$_GET['discount_code'] 		= $code;
			$_POST['discount_code']		= $code;
		}
	}

	// Have a discount code? Set the affiliate id
	if( ! empty( $_REQUEST[ 'discount_code' ] ) ) {
	
		$code = sanitize_text_field( $_REQUEST[ 'discount_code' ] );
	
		$code_id = $wpdb->get_var(
			$wpdb->prepare( "SELECT dc.id FROM {$wpdb->pmpro_discount_codes} AS dc WHERE dc.code = %s LIMIT 1", $code ) 
		);
	
		if( ! empty( $code_id ) ) {
	
			$affiliate = pmpro_ldc2aff_getAffiliateByCode( $code_id );
	
			$_REQUEST[PMPRO_LDC2AFF_KEY] = $affiliate;
			$_GET[PMPRO_LDC2AFF_KEY] = $affiliate;
			$_POST[PMPRO_LDC2AFF_KEY] = $affiliate;
		}
	}

}
	
add_action('init', 'pmpro_ldc2aff_init', 1);

/**
 * Show options on the Edit Discont Code page
 *
 * @param int $code_id
 */
function pmpro_ldc2aff_pmpro_discount_code_after_settings( $code_id ) {
	$affiliate = pmpro_ldc2aff_getAffiliateByCode($code_id); ?>
<hr />
<h3>Affiliate</h3>
<php 
     printf( '<p>Link this discount code to an affiliate. Currently monitoring the "%s" parameter. When the affiliate ID is set, this discount code will be defaulted to be used at checkout, and when a discount code is used the affiliate ID will be set.</p>', PMPRO_LDC2AFF_KEY ); 
     printf( '<p><label for="pmpro_ldc2aff_affiliate">Affiliate ID:</label>' );
     printf( '<input type="text" id="pmpro_ldc2aff_affiliate" name="pmpro_ldc2aff_affiliate" value="%s" />', esc_attr($affiliate) );
     printf( '</p>' ); ?>
<hr /><?php
}
	
add_action('pmpro_discount_code_after_settings', 'pmpro_ldc2aff_pmpro_discount_code_after_settings');

/**
 * Save the options when an affiliate discount code is updated
 * @param int $code_id
 */
function pmpro_ldc2aff_pmpro_save_discount_code($code_id) {
	
	if($code_id < 1) {
		return;
	}
	
	$affiliate = isset($_REQUEST['pmpro_ldc2aff_affiliate']) ? sanitize_text_field( $_REQUEST['pmpro_ldc2aff_affiliate']) : null;

	if ( !empty( $affiliate ) ) {
		pmpro_ldc2aff_updateCode($code_id, $affiliate);
	}
}
add_action('pmpro_save_discount_code', 'pmpro_ldc2aff_pmpro_save_discount_code');

/**
 * Delete affiliate options when their discount code is deleted
 *
 * @param int $code_id
 */
function pmpro_ldc2aff_pmpro_delete_discount_code($code_id) {
	
	if($code_id < 1) {
		return;
	}

	pmpro_ldc2aff_updateCode($code_id, false);
}
add_action('pmpro_delete_discount_code', 'pmpro_ldc2aff_pmpro_delete_discount_code');